Contingencies and Regulatory Matters - Recovery Balance of Each Regulatory Clause - Gulf Power (Details) - GULF POWER CO - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Under recovered regulatory clause revenues, current
Loss Contingencies [Line Items]
Fuel Cost Recovery	$ 13	$ 0
Purchased Power Capacity Recovery	1	0
Environmental Cost Recovery	0	13
Energy Conservation Cost Recovery	1	4
Other regulatory liabilities, current
Loss Contingencies [Line Items]
Fuel Cost Recovery	0	15
Environmental Cost Recovery	$ 1	$ 0